On May 3, 2007, League of Conservation Voters President Gene Karpinski realized that the plan was working.

That morning, Sen. Barack Obama (D-Ill.), then a presidential contender, attached his name to a model piece of climate legislation that sought to bring U.S. carbon emissions down by an ambitious 80 percent by 2050. Not to be outdone, a few hours later, Sen. Hillary Clinton (D-N.Y.) hastily announced she’d support the same bill.

And with that, climate issues seemed — at long last — to have departed the realm of idealism and entered the more fruitful arena of politics, with its results-driven rules of engagement. Environmentalists would no longer have to appeal to politicians’ best instincts by promising they’d be saving future generations and doing the right thing for the globe. Instead, climate activists could draft more-persuasive allies of the electoral variety: fear, ambition and self-preservation.

“It really became a competition. That was the beauty of it,” recalled Karpinski. “This became an issue where they were competing to see who was the best.”

Yet as green activists converge on the 15th United Nations Climate Change Conference in Copenhagen, their sense of disappointment is palpable, even with the eleventh-hour decision by President Obama to attend the summit on Dec. 9. What was seen in the heady days of 2007 and 2008 as the likeliest venue for a new international agreement on carbon emissions now caps a year of mixed results. While the American political system has, in many ways, seen a total transformation in its capacity and willingness to tackle such a transcendent issue, some of the traditional obstacles remain — primarily the age-old laws of partisan politics and the limits on how much ambitious legislation Congress can absorb at one time.

At the apex of the 2008 campaign, with the League and other groups leaning hard on a crowded field of presidential candidates, and congressional Democrats shifting steadily toward the view that action would be required, a Democratic victory seemed likely to mean a treaty in the new president’s first year.

In retrospect, though, what had seemed like a political coup was just a partial victory. The populist organizing, the new rhetoric of green jobs and the long-term goals of the campaign season glossed over the concrete terms that have turned 2009 into a season of diminished expectations, making clear that Copenhagen will be, at best, just another step in a long process. In interviews, environmental leaders made the case that the movement’s successes vastly outweigh the setbacks and that they probably never could have predicted the main obstacle to passing major climate legislation this year.

“When someone asks why aren’t we going to get a deal in Copenhagen, the biggest reason comes down to two words: health care,” said Karpinski.

If the green community is slightly downcast on the eve of Copenhagen, its members still argue that the 12-day conference should set the stage for a major showdown over climate legislation in Congress next year, with victory there being the precursor to a global accord.

“The president is working closely with Congress to pass energy and climate legislation as soon as possible,” the White House said in announcing his trip to the summit. Obama hopes his attendance will “drive progress toward a comprehensive and operational Copenhagen accord” that will “serve as a steppingstone to a legally binding treaty.”

At the beginning of Obama’s presidency, the House of Representatives chose to tackle climate change first, moving swiftly to pass legislation on carbon emissions last summer. But the White House — and, just as crucially, the Senate — went another way. In April, the Senate moved to reserve the procedural fast track known as reconciliation for health and education policy — but not for climate change.

“The administration looked at that and said, ‘We can’t get a clean win here. Let’s go for a clean win. Health care’s a clean win,’” said Sierra Club Executive Director Carl Pope. Even then, health care legislation “turned out to be a harder win than they thought,” he said.

The shift left environmental leaders frustrated and doubting the value of some early commitments.

“I do regret that when Obama made his original short-term commitment, we didn’t try to get him to be more ambitious,” Pope said, referring to Obama’s campaign promise to reduce emissions 17 percent by 2020 — a goal that because of the recession and state initiatives could today conceivably be reached without federal action.

“Hillary never trumped him on the short-term goal, so he never had to move it,” said Pope, who called Obama’s target “pathetically inadequate.”

The White House says Obama will offer the 17 percent cut below 2005 emissions during his trip to Copenhagen if China and other less developed countries offer “robust mitigation contributions” of their own.

A day after the president’s announcement, China declared that, by 2020, it would reduce emissions relative to its economic output by 40 percent to 45 percent compared with 2005 — a formula that would allow emissions to grow but slow the rate of increase.

Indeed, in the run-up to Copenhagen, countries from Russia to Brazil committed to more aggressive 2020 targets, and climate activists now are pushing the United States and other industrial countries to reduce their emissions by between 25 percent and 40 percent from 1990 levels.

With that focus on long term over short came a decision to stress the targets over the mechanics, including how to achieve such deep cuts and how much it would cost.

“They weren’t sweating the details,” said Chris Tucker, a spokesman for oil and gas industry groups that have fought efforts to regulate carbon emissions. “They were worrying about the aspirational and emotional stuff. And it turns out people care about the details.”

Advocates for a strong international treaty on carbon emissions continue to wrestle with a deep disconnect between a cultural moment — in which “green” is both a pop phenomenon and a corporate branding gimmick — and deep congressional skepticism toward actual action. Even oil companies pine for the green brand, and it’s almost undoubtedly good public relations for the major companies that have stormed out of the Chamber of Commerce because of its opposition to climate legislation.

But the green movement also has been unable to translate the broad popular support for environmental causes into a practical solution that captures the public’s imagination and could translate into legislative victory. The mechanism for controlling carbon emissions, known as cap and trade, has turned into an Achilles’ heel. And Copenhagen remains, to most Americans, merely the capital of Denmark. At best.

“There are a lot of people in the United States who hear the word ‘Copenhagen,’ and they think of chewing tobacco,” said Tucker, referring to a popular American brand. “There was a disconnect between the folks in Washington and the people on whom this was going to be imposed, and it should have been understood from the start that this was going to be a much heavier lift.”

But saving the planet didn’t seem too heavy a lift for Democrats campaigning in Iowa in 2007. Throughout the Democratic primary, environmental issues were prominent, and candidates were aggressive. If Clinton and Obama could promise an 80 percent reduction in emissions, New Mexico Gov. Bill Richardson would distinguish himself by going to 90 percent. This was no accident: The League of Conservation Voters and its allies had invested deeply in organizing in the early-primary states, making sure that the candidates would be grilled on climate issues at town halls and kitchen tables and that attention would be drawn to those who strayed from the vision of the man who, at the time, was the party’s most prominent leader, former Vice President Al Gore.

In August, the League aired a television ad in Des Moines, Iowa, that tinted the candidates’ faces green and that asked — amid chatter about the first black or first female president — who would be the “first green president.”

And then there were the turbines. Windmills were everywhere — at least, everywhere in the television ads candidates ran with promises to revitalize the economy through new, green jobs, the win-win argument developed by Democrats to sell environmentalism to blue-collar workers. That trend had begun in 2006, when the turbine was the “single most common symbol in a political ad,” said Sierra Club’s Pope.

“All over the country, people were running ads of wind turbines — and winning,” he said. “Americans really bought — probably even more than is true — the notion that clean energy jobs can’t be outsourced.”

Obama’s campaign seemed to vindicate the claims of environmentalists about a changed political environment on climate change when Clinton and Sen. John McCain, the GOP presidential nominee, responded to high gas prices by calling for a gas tax holiday.

“This isn’t an idea designed to get you through the summer; it’s an idea designed to get them through an election,” Obama said, successfully dismissing the notion as political gimmickry.

Obama’s victory in the presidential race underscored the importance of the environmental movement’s early organizing. He had once been a friend of the coal industry in his home state, Illinois, lavishing praise on “clean coal” technology that environmentalists considered little more than an excuse to keep polluting. But he quietly reversed that stance, stressing that clean coal was merely an ambition worth funding. He campaigned hard on global warming, made the phrase “planet in peril” part of his stump speech and turned the fight against climate change into one of the three pillars of his domestic platform.

Presidential politics wasn’t the only place the environmental groups were active. Led by Greenpeace, many activists focused on Congress, running grass-roots campaigns in local districts to pressure lawmakers to back climate legislation that was coming down the pike. The group persuaded 72 members of the House to more forcefully back action on climate change, said Phil Radford, Greenpeace’s executive director.

The Democrats’ electoral victories in November 2008 were, for the greens, a moment of triumph. In retrospect, however, the movement already was swimming upstream. The economic meltdown pushed climate change — an issue on which voters typically express concern, but not as a top priority — further down the public’s agenda.

The Pew Research Center found that by last January, global warming “ranked at the bottom of the public’s list of policy priorities for the president and Congress this year.” Independent voters and Republicans ranked it last on a list of 20 priorities, while Democrats ranked it 16th.

Other polling suggests Americans are growing more skeptical of the science behind climate change, with those who blame human activity for global warming — 36 percent — falling 11 percentage points this year, according to Pew.

That skepticism is likely to increase following the embarrassing leak last month of e-mail exchanges among climate scientists dissing the work of peers who doubt that humans are causing global warming.

Those public opinion numbers put the U.S. out of step with its major industrialized partners, Japan and the European Union, and closer to the lower-emitting countries of the developing world.

“The public is in favor of this so long as it doesn’t cost anything,” said David Victor, a Stanford Law School professor who has argued that the Copenhagen meeting should focus on concrete, politically plausible goals, not a global treaty. “Support was high until a year and a half ago, and then the collapse in the economy happened and got people focused on other things.”

“People wanted jobs right now,” said Pope. “The administration actively, eagerly wanted to put more of the stimulus money into short-term, fast-start green infrastructure, and they couldn’t, because the states hadn’t teed it up.”

“The timing was terrible,” he said. “And the timing of Copenhagen was terrible.”

By November, when the White House formally abandoned efforts to create a binding international treaty in Copenhagen, that outcome had been clear to both sides for months. The Senate now has pushed environmental legislation back behind financial reform, to next spring at best, eating away at American leverage overseas.

“The whole thing reminded me of the situation where you’re telling everyone you’re going to get married, you announce the wedding date, you choose your venue, pick the menu, invite all your friends — all without getting engaged, even without going on the first date,” said Tucker, the industry spokesman.

Privately, environmentalists are arguing among themselves about whether to publicly turn up the heat on the Obama administration, but they are reluctant to do anything that could weaken the president ahead of the climate debates on Capitol Hill. And Democratic officials have begun to express disappointment with the blown deadline.

“Countries see the United States not moving, and they wonder why they should do anything,” Sen. John Kerry (D-Mass.) told POLITICO. “They want to know where we are. Everybody asks, you know, ‘Are you going to act? What are you going to do? When are you going to do this?’”

Expectations remain low for Copenhagen, but there are signs that the climate issue is inching up on Obama’s agenda, including his decision to attend the conference and offer specific cuts in U.S. emissions.

Obama made climate talks a priority in a November visit to China, and there are signals that the United States may commit more aid to developing economies to help them meet their emissions targets. His administration, meanwhile, has moved fast on administrative measures that will make the U.S. targets easier to meet.

“You have to lower expectations [for Copenhagen] a little bit from what we would have liked to have seen happen,” said the League’s Karpinski. “We’ll be disappointed that we won’t get the final deal we want in Copenhagen, but we’ll make significant progress and put in place key building blocks.”

Other groups continue to keep the pressure on the president. Greenpeace recently unfurled a banner with his image from atop Mount Rushmore — a statement, it said, to suggest that he could be a truly great president, but only if he leads on the climate issue.

A political agreement short of a treaty in Copenhagen, Kerry said, could be an assertion of the president’s primacy over a recalcitrant Congress.

“It’s a restatement of the power of the president to direct the [Environmental Protection Agency] to regulate greenhouse gases. He has the power of the budget to make requests of Congress, he has the power of executive orders to order certain behavior in the transformation of energy in buildings, fleet purchases,” said Kerry. “But the main thing is that the president is committing to move in a direction, and, of course, where Congress and parliaments need to be brought into play, they are going to be brought into play.”

Greenpeace’s Radford said Obama’s problem is not his position on the climate issue but, rather, his will.

“The question is how much the president will lead,” he said. Americans have “overlearned” the lessons of Kyoto, where President Bill Clinton agreed to a treaty that he never submitted for ratification because it faced near-unanimous rejection in the Senate, Radford said.

“They’re using that as a reason to hide behind Congress instead of to lead Congress,” he said. “The world is watching to see whether [Obama will] step up.”